A charge pump circuit is a basic block of a flash memory and greatly affects the flash memory's program/erase speed. The continuous advancement of integrated circuit (IC) fabrication technology and our relentless pursuit for lower power consumption lead to the development of ICs powered by increasingly lower supply voltages.
On the other hand, in flash memories, program/erase operations of a cell still require relatively high voltages. In such a context, more and more importance is being attached to charge pump circuits in the continuously-developing IC domain. Currently, charge pumps have become a focus of research efforts in the field of flash memory design.
A charge pump, also known as a switched-capacitor voltage converter, is a kind of DC to DC converter that uses so-called “flying” or “pumping” capacitors (rather than inductors or transformers) for energetic charge storage to raise, lower an input voltage or to produce a negative voltage. An internal field effect transistors (FET) switch array of the charge pump controls transfer of electric charges among the capacitors in a certain manner (usually, uses clock signals to control the charge/discharge of the capacitors) so that the input voltage is raised (or reduced) in a certain way to a desired output level.
When a memory is reading data, a charge pump therein provides the memory with a read current and a read voltage of about 5.5 V. Therefore, before the read operation begins, the charge pump needs to raise the voltage to 5.5 V to place the memory into a standby state. After the read operation commences, the memory switches to an active reading state. In the standby state, as the output voltage of the charge pump may experience drops due to leakage currents, a detection circuit is required to monitor the output voltage of the charge pump in real time so as to increase the output voltage when it drops below the read voltage. If the detection circuit is powered by a supply voltage of 5.5 V, it will require a relatively large current and thus consume a significant power.